Pulse stretcher



Jan. 25, 1955 J. v. HOLDAM, JR,, ETAL 2,700,732

PULSE S'I RETCHER Filed Dec. 18, 1945 INVENTORS JAMES VANCE HOLDAM JR.

LLOYD M JONES ATTORNEY United States Patent PULSE STRETCHER Jam s V.Holdam, In. Camb idge, Mas and Lloyd Jones, Los Angeles, Calif assianorby mesne m n s, to the United S ates of Ameri as rep esen by theSecretary of the Navy Application December .18, 194 S ria No- 8 3 C ams- (c1; 250-21) This invention relat s o Pulse stretches, par i ularlyhose which respond in tantaneou ly to bo h ncreases or decreases in thmagnitude of he pulses impre sed thereon.

In gun lay ng ad r quipm nt, it is necessa y to stretch each video pulseof a series until the ccurren of the succeeding video pulse in order tokeep up a reference frame corresponding to the envelope of the series ofvido pulses and thus maintain the voltage necessary to train the guns.This Pulse stretching has been accomplished by using a long timeconstant circuit in the output of a cathode follower or rectifier andutilizing the voltage existing across the time constant circuit tocontrol the grid of the electron tube of the succeeding amplifier stage.This met od has the disa van age f not being able instantanenously torespond to both increases and decreases in magnitude of the series ofpulses to be stretched. Due to the rectifying act on of the rectifier orcathode follower an increase in magnitude would instantaneously beindicated as a voltage increase across the time constant circuit, but adecrease in magnitude would not be registered until .the time constantcircuit had discharged :1 corresponding amount. To shorten the timeconstant of the circuit would render the pulse stretcher less effectiveas such, due to the voltage decrease in magnitude of the stretched pulsewith time. To overcome this, schemes were proposed to short the timeconstant circuit by a delayed trigger shortly before the occurrence .ofeach pulse of the series to be stretched and thus prepare the timeconstant circuit for the pulse. This had the disadvantago that thepulses were not stretched over the entire priod between pulses, and thata trigger circuit was required with the accompanying complexity.

It is accordingly an object of this invention to provide a pulsestretcher that responds instantaneously to both increases and decrea esthe magnitude of the pulses impressed thereon.

'It is a further object .of this invention to provide a pulse stretcherthat does not require a trigger circuit to respond instantaneously toboth increases and decreases in the magnitude of the pulses impressedthereon.

These and other objects will be more apparent upon consideration of thefollowing specification together with the accompanying drawing, whichdiscloses a circuit diagram of an embodiment of the invention.

In the drawing the series of pulses to be stretched is applied toterminal 10 to be impressed on the grid of electron tube 11 and providesuitable bias for this grid by means of the conventional grid biasingcircuit 12 associated therewith. Tube 11 has its anode and cathodejoined with a source of plate potential and ground by resistors 13 and14, respectively. Anode resistor 13 has a larger resistance than cathoderesistor 14. Thus the pulses produced at the cathode and platesimultaneously with each pulse impressed on the grid will have differentmagnitudes and opposite polarities. It is thus seen that tube 11functions as a phase splitter. The negative anode pulses will be greaterthan the positive cathode pulses, assuming that the pulses impressed onthe grid are positive.

A pair of rectifiers, in the instant embodiment diodes 15 and 16, haveone of their anodes and cathodes joined together, while the free cathodeof diode 15 is connected with the plate of electron tube 11 throughblocking condenser 17 and the free anode of diode 16 is con- 2,700,732Patented Jan. 25, 1955 t d di c ly to t e a od o el c on t 11- The joineanode nd ca h o d od s d 6 r connec d to r nd h ugh apa or 18 s d r nnow t e ct n o t e c u t al y d bed apac t r 1 l ha e ss m d a c a qu te rence in potential between the anode of tube 11 and the oathode o tb 1. There l be no p te ti l d p oss resistor 25 since capacitor 17 willreach a fully charged c nd ion i the n er al b t n c e ve Pu s sri r t happlic n of a pu e a ter na 1 the auode of diode 16 will be at some lowpotential, for example, ground potential if tube 11 is completely outoif, while the cathode of diode 16 will be at the potent al o h ch pa tr 18 s ha e Sin he de of diode 16 is negative with respect to thecathode, diode 18 will be nonconducting. Diode 15 will also be nonnd c gtor e reas n that th a de of d d is at the potential of the grid of tube19, while the cathode of diode 15 is at the potential of the cathode oftube 19 which i ssu e a P t nt al g y P s t e wi h espe t to he idhu e ct d of tub 5 s p sitive with respect to the anode, Assume for the momentth a p s i e pu se i appl ed to e in re l in a positive and a negativepulse appearing at the cathode and anode respectively of tube 11. Assumefurther ha t e pul e pp ar n a t e a od of be 1 s an amplitude greaterthan the potential to which capacitor 18 is charged. The anode of diode16 will then become positive with respect to the cathode and theresulting current flow through diode 16 will tend to charge capacitor 18to the potential of the cathode of tube 11. The negative pulse at theanode of tube 11 will be coupled through capacitor 17 to the cathode ofdiode 15, making the cathode of diode 15 negative with respect to theanode of this tube. Current flow through diode 15 is in a directiontending to reduce the potential on capacitor 18 and also to reduce thepotential on the capacitor 17. However, the potential on capacitor 18cannot be lowered below the potential of the cathode of tube 11 sincethe current flow through diode 16 will restore charge on capacitor 18removed by the current flow through diode 1 5. The net result is thatcapacitor 18 assumes a potential equal to the amplitude of the pulse atthe cathode of tube 11, and the capacitor 17 assumes a potential equalto the difference between the potential .on capacitor 18 and thepotential at the anode of tube 11 during the negative pulse ,at thisanode. Un der this condition, the difference in potential between thecathode of diode 15 and the cathode of tube 19 will appear acrossresistor 25.

Following the termination of the pulse at terminal 19, the anode ofdiode '16 becomes negative with respect to the cathode of this tube andthe cathode of diode 15 becomes positive with respect to the anode ofthis tube, thus blocking in the discharge path from capacitor 18. In theinterval before the next pulse is applied to terminal 10, capacitor 17will again be charged to the difference between the potential at theanode of tube 11 and the new potential at the cathode of tube 19. Thecharging of capacitor 17 takes place through resistors 13, 25 and 20.

Assume now that a second pulse is applied to terminal 10 and that thispulse has an amplitude such that the pulse at the cathode of tube 11 hasan amplitude less than the potential on capacitor 18. Under thesecircumstances, initially, the anode of diode 16 will still be negativewith respect to the cathode of this tube and no conduction will takeplace through diode 16. However, the cathode of diode 15 will becomenegative with respect to the anode of this tube since diode 15 is heldnonconducting only by the amount of the grid to cathode bias on tube 19.Diode 15 will then conduct causing capacitor 18 to discharge throughdiode 15. When the potential on capacitor 18 has dropped to thepotential at the cathode of tube 11, diode 16 will begin to conductpreventing any further drop in the potential to which capacitor 18 ischarged. The operation of the circuit from this time on will beidentical to the operation as described in connection with theapplication of the first pulse to terminal 10. Since the diodes have alow resistance during conduction, the charging and discharging pathsincluding capacitor 18 will have an extremely short time constant duringoccurrence of the pulse to be stretched. This permits an extremely rapidresponse of the capacitor voltage to any change in the magnitude of thepulses applied at terminal 10.

An amplifier circuit including electron tube 19, cathode resistor 20 andanode resistor 21 is provided. The grid of tube 19 is connected directlywith the charged terminal of capacitor 13. Thus the voltage changesacross capacitor 18 appear amplified across resistor 21. A variable tapis provided on resistor 21 to permit abstraction therefrom of thedesired degree of voltage change to be impressed on the electron tube 22of the subsequent circuit, in the instant embodiment a phase splitter,Whose outputs are abstracted at terminals 23 and 24 for any desiredpurpose-here to control an indicator. Adjustment of the variable tappermits voltage changes to be secured thereat proportional to changes inthe magnitudes of the pulses of the series impressed terminal 10.

A leakage resistor 25 connects the cathode of diode 15 with the cathodeof tube 20. This resistor prevents the negative pulse from resistor 13from being shorted across resistor 20. The cathode of diode id isconnected thus to the cathode of tube 19 so that the cathode-anode biasof diode 15, necessary to prevent a leakage path for capacitor 18,remains essentially independent of the existing charge on capacitor 18.

Suitable values of certain of the circuit constants with conventionaltriode tubes have been found to be as follows:

Resistor 13-20,000 ohms Resistor 14-10,000 ohms Resistor 2150,000 ohmsResistor 25150,000 ohms Capacitor 17-.00l microfarad Capacitor 18-.0005microfarad The invention is only to be limited by the appended claims.

What is claimed is:

l. A pulse stretcher comprising, a phase splitter circuit, including anelectron tube having anode, cathode,

and grid, resistors joining said anode and cathode with a source ofplate potential and ground respectively, said anode resistor having alarger resistance than said cathode resistor, a pair of diodes having ananode and cathode of each joined together, a blocking condenser joiningthe free cathode of said pair of diodes with the plate of said electrontube, the free anode of said pair of diodes being connected with thecathode of said electron tube, a capacitor connecting the joined anodeand cathode of said pair of diodes with ground, an amplifier circuitincluding an electron tube having anode, cathode and grid, resistorsjoining said last mentioned anode and cathode with a source of platepotential and ground respectively, said last mentioned grid beingconnected with the joined anode and cathode of said pair of diodes, aleakage resistor connecting said free cathode of said pair of diodesWith the cathode of the electron tube in said amplifier circuit, and anadjustable tap on the anode resistor in said amplifier circuit, wherebythe voltage variation at said tap will be dependent on the magnitude ofthe pulses applied at the grid of the electron tube in said phasesplitter circuit.

2. A pulse stretcher comprising, a phase splitter circuit including anelectron tube having anode, cathode and grid, resistors joining saidanode and cathode with a source of anode potential and ground,respectively, said anode resistor having a larger resistance than saidcathode resistor, a pair of diodes, the anode of one diode beingconnected to the cathode of the other diode of said pair, a condenserjoining the free cathode of said pair of diodes with the anode of saidelectron tube, the free anode of said pair of diodes being connectedwith the cathode of said electron tube, a capacitor connecting thejoined anode and cathode of said pair of diodes with ground, anamplifier circuit including electron tube having anode, cathode andgrid, resistors joining said lastmentioned anode and cathode with asource of anode potential and ground, respectively, said last-mentionedgrid being connected with the joined anode and cathode of said pair ofdiodes and a resistor connecting said free cathode of said pair ofdiodes with the cathode of the electron tube in said amplifier circuit.

3. A pulse stretcher comprising, means for producing a pair ofsimultaneously occurring pulses of equal time duration in response to apulse applied thereto, said pair of pulses including a positive pulsehaving an amplitude proportional to the amplitude of said input pulseand a negative pulse, said positive and negative pulses appearing atfirst and second outputs of said pulse producing means respectively, apair of rectifiers each having an anode and a cathode, the cathode of afirst of said rectifiers being connected to the anode of a second ofsaid rectifiers, means conductively connecting the anode of said firstrectifier to said first output of said pulse producing means, a firstcapactior connecting said cathode of said second rectifier to saidsecond output of said pulse producing means, a second capacitorconnected between said cathode of said first rectifier and a point offixed reference potential, an amplifier circuit including an electrontube having an anode, a cathode and a grid, resistors joining saidlast-mentioned anode and cathode with a source of anode potential and apoint of fixed reference potential respectively, said grid beingconnected to the joined anode and cathode of said rectifiers, and aresistor connected at one end to said cathode of said electron tube andat the other end to the cathode of said second rectifier.

References Cited in the file of this patent UNITED STATES PATENTS

